Although the contactor is probably one of the most common components in an industrial / motor control application, selecting one correctly requires detailed application information to be provided.

There are 3 key elements to a contactor

• Main contacts (also referred to as main poles)
• Auxiliary contacts
• Coil (part of the electromagnet used to energise the contactor).

Each of these elements should be fully specified based on the application;

1. Main pole selection criteria

• How many required in either normally open (N/O) or normally closed (N/C) format
• Current rating in amps.
• Voltage rating in AC or DC
• Duty (either AC1, AC3, DC1- DC5 etc). In the absence of a specific duty, a full description of the nature of the electrical load (e.g. lighting , resistive heating etc), making current, breaking current and continuous current through the contacts.

2. Auxiliary contacts selection criteria

• How many required in either normally open (N/O) or normally closed (N/C) format. Possibility of time delayed auxiliary contacts with certain product ranges.
• If not used in standard low power signalling application, details as per main poles required.

3. Coil selection criteria

• Voltage of coil (Note: The coil is often a different voltage to the main poles).
• AC or DC voltage;
  • Frequency of coil if AC (Usually 50Hz or 60Hz)
  • If DC coil, is low consumption required (available for certain ratings of TeSys D and TeSys K contactors).

Any additional information available should be provided, for example

• Is the contactor to be enclosed, i.e. is an enclosed motor starter required?
• Specific design requirements (e.g. Modular)
• Number of operations per hour
• latching operation
• Environmental considerations such as ambient temperature etc.
• Are any ancillary parts required such as mechanical interlocks, busbars, thermal overload relays or motor protection circuit breakers?

Released for: Schneider Electric UK